Project Summary Sjgren?s syndrome (SS) is an autoimmune disease in which exocrine tissue is damaged, resulting in loss of tears and saliva. Primary SS (pSS) affects salivary and lacrimal tissue and results in many serious systemic disease manifestations. Once diagnosis is achieved, no SS-specific curative treatment options are available; rather treatments for SS are palliative. Thus, there is a critical need to identify etiologic events that will facilitate earlier diagnosis of SS and development of therapeutics that mitigate the progression of this debilitating disease. Studies in our laboratory revealed that Myeloid Differentiation Factor Primary Response Protein 88 (MyD88) is essential for pSS development. MyD88 is an adaptor molecule that is expressed ubiquitously and is required for most Toll-like receptor (TLR) and IL-1 receptor (IL-1R) family member signaling. Notably, TLRs and IL-1R family members are elevated locally (in salivary tissue) and in peripheral blood cells of SS patients, suggesting these receptors contribute to SS. Our central hypotheses are that (i) tissue-specific MyD88 expression dictates distinct pSS disease manifestations and that (ii) activation of MyD88-dependent signaling networks by the endogenous ligand Decorin (Dcn) drives pSS pathogenesis. Our objectives are to identify the tissue-specific contributions of MyD88 and to determine the MyD88-mediated signaling networks that govern pSS disease pathogenesis. We will employ a pSS mouse model (NOD.B10) and a conditional knockout strain of NOD.B10 mice developed in our laboratory that lacks expression of MyD88 in the stromal compartment (non- immune cells) specifically. These mice provide a unique model system to examine the role of MyD88 in pSS directly. The rationale for this proposal rests on the fact that activation of MyD88-mediated signaling pathways contributes to many autoimmune diseases. Both salivary tissue and immune cells express receptors that promote inflammation via MyD88, such as TLRs. Our studies in pSS mice deficient in MyD88 demonstrate that MyD88 is crucial for pSS pathogenesis; however, the specific cell types that express MyD88 in disease and the MyD88-dependent signaling pathways that are activated in pSS are incompletely understood. We will test our hypotheses by completion of two specific aims: (1) Identify stromal cell-specific contributions of MyD88 to pSS pathogenesis, (2) Evaluate Dcn-mediated inflammatory signaling networks in pSS. This study is innovative because it will uncover new mechanisms related to the role of MyD88-dependent signaling networks in pSS and will identify specific cell types that mediate distinct pSS disease manifestations. Targeted blockade of MyD88- dependent signaling pathways represents an innovative therapeutic approach for the treatment of pSS. This proposal is significant because it will reveal new mechanisms that govern chronic inflammation in pSS. Insights obtained from the proposed studies will reveal novel pathways and specific cell types that can be targeted to treat pSS and other autoimmune diseases.